Some notes:
Hardforks like Bitcoin ABC without a malleability fix are very unlikely to
have payment channels, so the problem does not exist for those.
The designers of a hardfork which does have a malleability fix will
probably know about payment channels, so they can just build a replay
As soon as there is competition for block space, people will likely
outsource creating the proof of work on the transaction to "transaction
miners". This would likely result in giving a fee to those transaction
miners. If those are the same miners as those mining the block, we are back
at the
